Order, Chaos and the Space Between the Stars

Alyssa A. GoodmanHarvard-Smithsonian Center for Astrophysics

WIYN Image: T.A. Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)

Truth

Truth in (my) Science How does the gas between the stars arrange and re-arrange itself in the process of forming new stars?

Truth in Religion What does it mean to lead a “good” life?

History + Principles — Dogma = Truth

Dogma

The word dogma (Gr. dogma from dokein) signifies, in the writings of the ancient classical authors, sometimes, an opinion or that which seems true to a person; sometimes, the philosophical doctrines or tenets, and especially the distinctive philosophical doctrines, of a particular school of philosophers (cf. Cic. Ac., ii, 9), and sometimes, a public decree or ordinance, as dogma poieisthai.

History + Principles — Dogma Truth

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History + Principles — Dogma Truth

…as applied to the formation of new stars,

&the observation of magnetic fields in star-

forming regions

Tonight

Order

WIYN Image: T.A. Rector, B. Wolpa and G. Jacoby (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)

Chaos

Molecular or Dark Clouds

"Cores" and Outflows

“Order”

Jets and Disks

Extrasolar System

1 p

c

Magnetic Dogma,c. 1985:

Order

(or)

Disk + Star

Core

Dark Cloud, Theory #2

Dark Cloud, Theory #1

A Truly Theoretical Set of Polarization Maps

Outflows

MagnetohydrodynamicWaves

Thermal Motions

MHDTurbulence

InwardMotions

SNe/GRBH II Regions

ChaosB

The Truth: Order in a Sea of Chaos

"Rolling Waves" by KanO Tsunenobu © The Idemitsu Museum of Arts.

The “Truth” about Interstellar Magnetic Fields

HistoryCosmic rays, synchrotron emission, polarization, Zeeman

effect

PrinciplesMaxwell’s Equations + Fluid Equations = “magnetohydrodynamics” [MHD], Gravity

DogmaFlux-freezing, Aligned Grains, The Angular Momentum

Problem, Outflow Confinement, and other Words of the Wise

TruthA difficult-to-measure and “messy” field whose role varies

depending upon conditions. “Ongoing cosmic creativity.” (G. Kaufman)

Pre-1980 History of B in the Galaxy

1949 discovery of polarization of background starlight (Hall, Hiltner)

1950 observational/theoretical understanding of cosmic ray confinement & strength of magnetic field in the Milky Way (Chandrasekhar, Fermi, Kiepenheuer, Spitzer)

1950+ optical & radio recognition of “synchrotron” emission

1950 interpretation of polarization as due to magnetically-aligned dust in space (Davis & Greenstein)

1968 Zeeman effect (direct measure of field strength) detected for the 1st time--strength as “predicted” (Verschuur)

1970’s large-scale mapping of “background starlight” polarization

Pre-1980 History Relevant Tonight

1949 discovery of polarization of background starlight (Hall, Hiltner)

1968 Zeeman effect (direct measure of field strength) detected for the 1st time--strength as “predicted” (Verschuur)

1970’s large-scale mapping of “background starlight” polarization

Principles: Gravity & Electromagnetism

1873 Maxwell publishes his unifying theory of electrodynamics, which is expressed in just four equations

1943 Alfvén publishes “On the Existence of Electromagnetic-Hydrodynamic Waves”

1687 Newton publishes the Principia, setting out his theory of gravity

Principles: Fluids

1851 Stokes publishes “Navier-Stokes equations describing a “laminar” flow

1975 advent of “numerical simulations” of turbulent flow (Woodward publishes first hydrodynamic simulation of a molecular cloud (using bomb codes))

1990’s 1st “magnetic” simulations carried out Woodward 1976

Outflows

MagnetohydrodynamicWaves

Thermal Motions

MHDTurbulence

InwardMotions

SNe/GRBH II Regions

What is the true role/shape of the

magnetic field here?

One more bit of History (which later, unfortunately, became Dogma)

AG’s Ph.D. thesis (1989) work showed…– Historical B-field measurements were, in

Principle, consistent with a picture where B is strong enough to matter in cloud dynamics

– New B-field measurement (just one!) confirmed this hypothesis

“Dogmatic” view of “energetically significant” magnetic fields

Outflows

MagnetohydrodynamicWaves

Thermal Motions

MHDTurbulence

InwardMotions

SNe/GRBH II Regions

What is the true role/shape of the

magnetic field here?

The History of a Star/Disk/Outflow System

figure

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et a

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98

4

Mapping Magnetic Fields: “Background Starlight Polarimetry”

Background Star emitsUnpolarized Continuum

Result: Observed -vector is parallel to plane-of-the-sky component of .

EB

B

Most LikelyOrientation

Least Likely Orientation

Polarization of Background Starlightby Magnetically Aligned Grains

E

B

(Partial) Polarization Observed

Rorschach Test

Dogma, c. 1985

(or)

Disk + Star

Core

Dark Cloud, Theory #2

Dark Cloud, Theory #1

A Truly Theoretical Set of Polarization Maps

Principle or Dogma?Dark CloudAmbient ISM Ambient ISMCloud Envelope

1A = 5 >10 5 1 mag

Cloud Envelope

Background Star Observer

Dark Cloud is a Local Denisty Maximum along l.o.s. --so the polarization observed gives B-field THERE

"Dark Cloud"

Densi

ty

Distance along Line of Sight

Recall the Dogma

Uchida & Shibata 1985

Does this violate Dogma, Steve?

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Dark C

lou

d C

om

ple

xes: 1

-10

pc sca

les

Dark C

lou

d C

om

ple

xes: 1

-10

pc sca

les

B216-217

Cold Dark Clouds: Looking Inside(?)

Goodman et al. 1992

What if…Not all Grains are Created Equal?

Less

Dust

, Much

Pola

rizat

ion

Much D

ust,

no Po

lariz

ation

Less

Dust

, Much

Pola

rizat

ion

Goodman et al. 1995

Dark CloudAmbient ISM Ambient ISMCloud Envelope

1A = V

5 >10 5 1mag

Changes in the Efficiency of Polarization Along a Line of Sight

Densi

ty

Distance Along Line-of-Sight

Pola

riza

tion E

ffici

ency

Polarization Efficiency Drops w/in

"Dark Cloud"

"Dark Cloud" is a Local Density

Maximum Along l.o.s.

Cloud Envelope

Background Star Observer

"Dark Cloud"

Result: “Pioneering a Dead End”

A V[magnitudes]

Pola

rizt

ion [

%]

?

Polarization May Show

NO Increase with

Extinction!

"Dark Cloud" Affects the Extinction, but NOT the Polarization

Pola

riza

tion [

%]

Cold Dark Clouds: (Not) Looking Inside

3

2

1

0

1086420

Extinction [mag]

B216-217 (Goodman et al. 1992)

L1755 (Goodman et al. 1995)

Galaxy (Jones, Klebe & Dickey 1992)

Fit to these dark clouds

More StuffAm

ount

of

Pol

ariz

atio

n

New History: Background Starlight Polarimetry cannot probe B-field “inside”

Dark Clouds

Not S

ensit

ive to

B-F

ield

Her

e

What does that mean?

Dark C

lou

d C

om

ple

xes: 1

-10

pc sca

les

“Go no further than AV~1.3 mag.”

3.0

2.5

2.0

1.5

1.0

0.5

0.0

PR

[%]

43210

43210AV [mag]

Background to Cold Dark Cloud

Arce et al. 1998

Background to General ISM

A Better Path to Truth? Look at the Grains’ Own Emission

Result: Observed -vector is perpendicular to plane-of-the-sky component of .

EB

B

Most LikelyOrientation

Least Likely Orientation

E

B

(Partial) Polarization Observed

©National Geographic

The “Canonical” Example: Orion

Clinging to Dogma?

Schleuning et al. 1998

HST/NICMOS

What is the field doing?

Figure from: Kannappan & Goodman 1998

What is the field doing?

Figure from: Kannappan & Goodman 1998

HII Region

Does Any Polarimetry tell “The Truth”?

Does polarization map give true field structure?

Polarization drops as density increases (similar to

background starlight story)

Plots and data from Henning, Wolf, Launhart & Waters 2001

Simulated Truth3D MHD simulation of Gammie, Stone & Ostriker

Field lines“look” straight-ish,even thoughB is significant.

Simulated Truth

C2

C3

C1

Padoan, G

oodm

an, D

rain

e, Ju

vela

,Nord

lund, R

ögnvald

sson 2

00

1

3-D simulation•super-sonic•super-Alfvénic•self-gravitating

Model A:Uniform grain-alignment efficiency

Simulated Truth

Padoan, G

oodm

an, D

rain

e, Ju

vela

,Nord

lund, R

ögnvald

sson 2

00

1

3-D simulation•super-sonic•super-Alfvénic•self-gravitating

Model B:Poor Alignment at AV≥3 mag

C2

C3

C1

AV,0 =3 mag

Dense Cores

Core C1

Core C2

Core C3

Core C1; AV,0=3 mag

Core C2; AV,0=3 mag

Core C3; AV,0=3 mag

Padoan, G

oodm

an, D

rain

e, Ju

vela

,Nord

lund, R

ögnvald

sson 2

00

1

Polarization vs.

How Much Stuff

0.0 0.2 0.4 0.6 0.8 1.0I/Imax

0

2

4

6

8

10

12

Core C1y

0.0 0.2 0.4 0.6 0.8 1.0I/Imax

0

2

4

6

8

10

12

Core C1y(AV,0 =3 mag)

0.0 0.2 0.4 0.6 0.8 1.0I/Imax

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Core C2y

0.0 0.2 0.4 0.6 0.8 1.0I/Imax

0

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4

6

8

10

12

Core C2y(AV,0 =3 mag)

0.0 0.2 0.4I/Imax

0

2

4

6

8

10

12

Core C3y

0.8 1.0I/Imax

0

2

4

6

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10

12

Core C3y(AV,0 =3 mag)

Pad

oan

, G

oodm

an

, D

rain

e, Ju

vela

,Nord

lund

, R

ögnvald

sson

20

01

Observations + Theory — unfounded generalization = Truth

History + Principles — Dogma = Truth

Dynamic Creativity

work in progress by Bate, Bonnell & Bromm